folder-transfer v0.13.0

Changed

• Parallel mode now shards by fine‑grained work units (bundles / large files), not whole
  folders. A single producer lazily walks the source and feeds a bounded shared queue; the N
  connections pull units until it's drained. Result: even one giant folder now spreads across all
  streams automatically — no need to split it into separate folders entries for balance.
• Mirror is exact again in parallel mode. All streams record what they received into one shared
  set; after every stream finishes cleanly, the receiver does a single reconciliation pass and
  deletes any local file the source no longer has — including files under a whole top‑level folder
  removed on the source. This removes the v0.12.0 limitation where vanished top‑level folders were
  not pruned in parallel mode. If any stream drops, the run is treated as incomplete and nothing is
  deleted that time (re‑run to complete). As before, the mirror deletes files, not directories.

Fixed

• Parallel server handlers initialise their progress timers before sending, fixing an
  op_Subtraction error that could abort sends (and write 0‑byte files) under the new unit model.